1. Field of the Invention
This invention relates to an aqueous ink which contains water, a water-soluble organic solvent and a pigment. Specifically, it relates to an aqueous ink which is suitable for recording methods and a recording apparatus making u se of an ink-jet method, i.e., ink-jet recording methods (image forming methods or recording methods), and to an ink-jet recording methods, an ink cartridge, a recoding unit, an ink-jet recording apparatus and an image forming method which make use of the aqueous ink.
2. Related Background Art
Conventionally, inks which contain pigments as colorants (pigment inks) are known to form images having good fastness such as water resistance or light resistance. In recent years, various techniques have been proposed for the purposes of improving the print density of images formed using such inks and, where color images are recorded such that areas having colors different from one another stand adjacent, more effectively keeping color mixing (bleeding) from occurring at the boundary areas of respective-color images.
For example, it is proposed to achieve significant improvement in image density by the use of an ink containing a self-dispersible carbon black and a specific salt (see, e.g., Japanese Patent Application Laid-open No. 2000-198955). A technique is also proposed in which an ink-jet recording ink which is a composition containing a pigment, fine polymer particles a water-soluble organic solvent and water and an aqueous solution containing a polyvalent metal salt are adhered to a recording medium, and the ink composition is allowed to react with the aqueous polyvalent metal salt solution to form high grade images (see, e.g., Japanese Patent Application Laid-open No. 2000-63719) In both of these techniques, the pigment present in the ink is in a dispersed state and forcedly made to flocculate on the recording medium surface to thereby keep the pigment from penetrating into the recording medium to obtain images having a much higher density and to prevent bleeding.
In addition, since in the pigment inks the pigment is made to flocculate on the recording medium, the pigment tends to remain on the surface of the recording medium. In particular, where the pigment ink is used to print images on plain paper, blurring may occur when the print surface is strongly scratched, even after a sufficient time has lapsed from printing, or print blurring may come about when something is written with an aqueous ink marker on images after printing. That is, pigment inks have a problem in that they have poor scratch and marker resistance.
Previously, some efforts have been taken for the purpose of improving scratch resistance. For example, it has been proposed that scratch resistance can be improved by adding a water-soluble emulsion to a self-dispersion type pigment ink (see, e.g., Japanese Patent Applications Laid-open Nos. H03-56573, 2001-329199 and 2001-329200).